AN APPLICATION OF REMOTLEY CONTROLLED

EXPERIMENTS TO PERFORM FEEDFORWARD AND

FEEDBACK DAMPING CONTROL OF AN ELECTRO

MECHANICAL SERVOMECHANISM

Andrew P. H. Weightman, Peter R. Culmer, Martin C. Levesley

School of Mechanical Engineering, The University of Leeds, Leeds, United Kingdom

Ben Hanson

School of Mechanical Engineering, University College London, London, United Kingdom

Keywords: e-Learning, Remotely Operated Experiments.

Abstract: This paper presents the findings of a pilot study to examine the possibility of delivering a control and

dynamics laboratory session, using equipment located at the University of Leeds, to students at University

College London (UCL), utilising the ReLOAD (remote access to real experimental equipment) system. The

ReLOAD system has been developed to provide improved access to experimental equipment, used as part of

undergraduate engineering degree programmes. Key to its operation is the availability of the system to serve

video clips that record the experiment in progress, providing essential visualisation plus an improved sense

of realism for the user. Students at UCL remotely performed an experiment to determine the effect of

varying the feedforward and feedback gain on the dynamics of an electro mechanical servomechanism.

Evaluation of the ReLOAD system, performed by the module leader at UCL, shows the system has huge

potential to allow more efficient and collaborative use of laboratory equipment across the global

engineering education community.

1 INTRODUCTION

Laboratory based teaching sessions are a key

element of teaching engineering during an

undergraduate degree program in the United

Kingdom. These laboratory sessions provide an ideal

opportunity to enthuse, motivate and inspire students

through face-to-face interaction with teaching staff

and real experimental equipment. However these

sessions are costly, both in terms of equipment and

time taken by teaching staff to deliver them. In the

UK, a typical face-to-face session may last 2-3 hours

and consist of a group of 20-30 students, working in

pairs or small groups within a laboratory

environment. Often multiple copies of experimental

equipment are required for these laboratory sessions,

limiting the quality of the equipment that can be

deployed. Even with group sizes of 20-30 students,

laboratory sessions often need be repeated many

times in a given year to ensure all students on a

particular program are exposed to the session. Even

with multiple copies of equipment and duplicate

laboratory sessions, students can find that access to

equipment is limited, as often the laboratory is

running a different class or teaching staff are

attending to other commitments. Students can

potentially miss out on laboratory sessions due to

illness, or be prevented from repeating a laboratory

session to collect more data because of such

restrictions. Laboratory sessions can be viewed as

being inefficient, since although expensive

equipment is used intensively for a period, it may

remain unused for most of the year.

In 2000, to overcome some of these limitations,

a system called ReLOAD (Real Labs Operated at

Distance) was developed within the School of

Mechanical Engineering at the University of Leeds,

which allows access to experimental equipment via a

web interface. Although the system cannot be used

to develop practical skills such as the use of

equipment, it does allow students to develop skills

such as planning experiments, collecting and

419

P. H. Weightman A., R. Culmer P., C. Levesley M. and Hanson B. (2007).

AN APPLICATION OF REMOTLEY CONTROLLED EXPERIMENTS TO PERFORM FEEDFORWARD AND FEEDBACK DAMPING CONTROL OF AN

ELECTRO MECHANICAL SERVOMECHANISM.

In Proceedings of the Third International Conference on Web Information Systems and Technologies - Society, e-Business and e-Government /

e-Learning, pages 419-426

DOI: 10.5220/0001278204190426

 SciTePress

analyzing data, and conducting further experiments

if required. It offers greater accessibility, can be run

24 hours a day, 365 days a year and allows many

students to access a single piece of high quality

equipment.

Other institutions across Europe the United

States, Australia, Asia etc. are also developing

similar systems to allow web based access to

experiments, many as part of consortia, to promote

sharing of equipment. Like the MIT iLabs system,

ReLOAD has been used recently to allow students

from one institution to use equipment in another,

many time zones away. This enables the system to

be used at times when normally it would be

underutilized. In some of the systems developed,

attempts have been made to reproduce face-to-face

laboratory sessions as closely as possible, in some

cases by employing technician staff to be available

in the laboratory at a prearranged time, to help

conduct the experiment remotely using

telecommunication links. In contrast to this

approach, ReLOAD aims to convince students that

this is a physical experiment and not just a

simulation, by providing highly visual experiments

with the content being visualized using video clips

taken from a webcam. It is an important aspect that

students should be able to perform the entire

experiment, without the need for technician

intervention, allowing the experiment to be

undertaken at a time that suits the student. This

approach is the same as that adopted by the State

University of New Jersey (RUTGERS), amongst

others.

The ReLOAD system is now sufficiently

developed to allow the pilot study presented in this

paper to be conducted, which examines the system’s

suitability as an e-learning tool. Student feedback

has so far been very positive, with students

particularly appreciating the virtually unlimited

access and the ability to easily visualize the output

via the use of the video clips, simultaneously with

near real-time analogue data and the reinforcement

of the sense that they are accessing real experimental

data that these clips provide.

2 RELOAD SYSTEM OVERVIEW

The idea of remote access to experiments is that the

physical experimental equipment does not need to be

in the same location as the person performing the

experiments. Hence a greater flexibility in

performing experiments is gained, although there is

the danger the user may doubt the realism of the data

or feel detached from the experiment being

performed no matter how good the interface (Selmer

et al., 2005). The Internet or LAN network is ideal

for the transfer of data in such cases and though

several different methods can be employed to deliver

remote experiments, the basic structure adopted here

is as shown in figure 1 (Levesley, 2006).

Figure 1 illustrates that a client computer can

send a request to a central web server (the ReLOAD

web server) for experimental data across the Internet

from any location with an Internet connection. The

ReLOAD web server interprets the request and

redirects this request via a LAN to one of several

Experiment Server computers physically connected

to either single or multiple pieces of experimental

Internet

Client

computer

ReLOAD

Web Server

Experiment

Server 1

Equipment 1.1

Equipment 1.2

Hard Wired

Connection

Experiment

Server 2

Equipment 2.1

Equipment 2.2

Figure 1: ReLOAD Remote Experiment Structure.

LAN

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equipment. The request is then converted into a

series of commands appropriate for the specific

equipment being run by the Experiment Server.

When the experiment requested is completed the

Experiment Server computer sends results in the

form of data images and video clips back to the user

on the client computer via the ReLOAD web server,

providing virtually the same level of information as

would be obtained by performing the experiment

locally.

2.1 The Web Server

The web sever is set-up to receive and process

requests from the client, and since the web server

can be a single computer, custom software can be

readily created and installed to monitor internet

requests. The client computer may be one of

hundreds of different PC's and the manner in which

data is transmitted and received from the client

computer has significant impact on the overall

functionality and versatility of the final system.

Several alternative methods have been proposed

previously. An Active-X control panel could be

installed on the client computer to send and receive

information (Hites, 2002) through an Active-X

enabled browser. Alternatively a Java applet could

be created to run on a standard Internet browser to

control the experiment (Rohrig & Jochheim, 1999,

Sanchez et al., 2000). The ReLOAD system

simplifies all aspects of the remote experiment to

create a reliable, maintainable system. A standard

web form is used at the client end to request

experiments and retrieve and view the associated

results. At the server end, LabVIEW software

performs the experiments while monitoring,

receiving and sending data across the internet to the

client computer. The client computer only requires

standard java support to view the video feedback.

2.2 Controlling Equipment

The Experiment Server computers perform the

experiments and communicates across a LAN and in

turn pass the data on via the internet to the client PC.

Using data acquisition hardware, LabVIEW

software is used to control the experimental

equipment. The use of a single programming

environment and language simplifies the

development process.

The front panel of the Experiment Server

computer displays all parameters used by the

experiment, together with a preview window for the

video camera and the results graph. Hence the

experiment server computer functions as a

demonstration display, allowing staff, students and

visitors within the School of Mechanical

Engineering in Leeds to observe the experiments

being requested remotely. A tabbed panel on the

computer displays either a log of the requests

submitted to the system or the setup panel. A

shutdown button is incorporated into the design such

that it ensures that any requests being processed are

first dealt with before the ‘shutdown’ state.

2.3 System Communication

LabVIEW allows two alternative methods to

communicate the required information between

computers to perform remote experiments LabVIEW

HTTP Server with Common Gateway Interface

(CGI) Scripts or embedded ActiveX control panels.

The LabVIEW Web Server and embedded panel

method has several shortcomings. Firstly, it would

be necessary to purchase as many licenses as the

number of users that may be expected on the

experiment. Secondly, the provision of video; since

continuous experimental interaction is possible it

would be consistent to use streaming video footage,

giving a ‘live’ indication to the state of the

experiment. However, the quality of the video

footage is dependant on the connection speed.

Finally, this method relies on proprietary plug-ins in

order to embed the VI’s panel in a web-page.

The HTTP Server with CGI scripts method does

not encounter these problems, and justifies its use

for this application. The HTTP server does not

require a license dependant upon the number of

users expected and only a widely supported, multi-

platform java plugin is required, in this case to

display the video. It is important to note that only

experiments not requiring continuous interaction are

possible using this method.

The LabVIEW Internet Toolkit, an add on to the

standard LabVIEW package, provides a HTTP

server and a set of related Virtual Instruments (VI’s).

VI’s is the term used to refer to units of code that

perform a particular function. Of particular

relevance to this application are the CGI script VI’s.

CGI scripts are typically used in association with a

form on a web-page. Forms are defined using

standard HTML elements and allow a user to enter

information into a number of fields and post it to a

server. The server receives the post and invokes the

relevant CGI script. The script then processes the

information and sends back a response, typically a

web-page, through the server to the user. Note, once

the user has posted a form the web-browser will

AN APPLICATION OF REMOTLEY CONTROLLED EXPERIMENTS TO PERFORM FEEDFORWARD AND

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421

await a response from the server and display it once

received.

It is possible to achieve the required interaction

between the user and the experiment by combining

the LabVIEW HTTP Server and the CGI script VI’s.

The experimental parameters can be entered into a

form on a web-page and posted to the LabVIEW

HTTP Server. This will then invoke a CGI script VI

that interprets these parameters and uses them to

conduct the experiment. The results will be returned

in the form of a web-page to the user when the

experiment is complete. This approach is illustrated

in figure 2. The CGI script VI’s can only be used in

conjunction with the LabVIEW HTTP Server. The

communication between the web browser and HTTP

Server can be over any network supporting HTTP

traffic, for example a departmental LAN or the

Internet. LabVIEW (8.0) contains tools aimed at

making it easier to control VI’s using a web-

browser. The front panel of a VI can be embedded

into a web-page. It takes the form of an ActiveX

component if Internet Explorer is being used, or a

plug-in for Netscape. The computer running the VI

must also run the LabVIEW Web Server which

controls communication between the embedded

front panel in the web-page and the actual front

panel of the VI. The user can view the front-panel or

request to control it. When viewing, the user sees a

‘live’ representation of the front panel. When

controlling, the user can do everything that would be

possible if using the actual VI, for example altering

controls or pressing buttons.

2.4 Experiment Request Control

As each experiment conducted will take a finite

amount of time, and multiple requests may be

submitted by different users at an instance in time, a

queuing system is used to ensure all experiments are

performed in an orderly manner.

Both incoming experiments and outgoing results

are stored in queues. When the server receives data

posted from the ‘input parameters’ web-page it is

added to the back of the request queue. When the

experimental apparatus is ready to conduct an

experiment it removes the oldest request from the

queue and uses the parameters given. The

experiment results are placed at the back of the

results queue once the experiment is completed.

Both queues operate on a first in first out basis. Each

item in the request queue contains a number of

elements. Firstly are the IP Address that the request

was submitted from and the CGI connection

information, such that the results can be sent back to

the user. The experiment name is sent as a text string

to provide for the possibility of running multiple

experiments on the same machine.

Finally, the parameters sent from the web-page

form are included as a keyed array. This is a cluster

of two arrays, the first containing the parameters

names (called keys) and the second their values. The

‘keys’ are simply the names given to the individual

fields in the web-page form. Each item in the

Results queue consists of two elements. Firstly the

CGI connection information required to send the

results back to the user. Secondly, a text stream

containing the results web-page location.

The queue size is limited to prevent large

numbers of requests amassing under heavy demand.

A default value of 10 was used for the maximum

number of requests in the queue, an acceptable

compromise between allowing multiple users and

minimizing the delay before results are returned. If

the queue is full when a request is submitted, the

user is sent a ‘busy’ web-page in reply, the request is

then discarded. A further check can be performed to

check if the IP address of a submitted request is the

same as one currently in the queue. If this is the case

the request is discarded and a single user is

prevented from dominating the queue system.

3 EXPERIMENTAL EQUIPMENT

The experiment chosen for this pilot study of

ReLOAD, to be remotely delivered to students on

E467 Automatic Control at UCL, was one which

Results

Experiment

Parameters

http://www.leeds.ac.uk/

Remote Control

Experiment

Amplitude 5.00

Frequency 100

Submit

LabVIEW

HTTP

Server

CGI Script

VI’s

Figure 2: ‘Labview HTTP server with CGI script’

method.

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422

enables investigation of the performance of a closed

loop position servomechanism, as the forward path

gain and the velocity feedback gain are varied. The

purpose of the servomechanism system is to keep

the angular position of the Output shaft (output dial)

in correspondence with that of a Reference or

Demand shaft. The purpose made equipment, used

for the remote experiment was designed and built by

staff and students of the School of Mechanical

Engineering at Leeds and is based on equipment

used in face-to-face laboratory sessions in the

second year of an undergraduate degree programme.

It comprises the Servomechanism (motor, position

potentiometer, tachogenerator etc) and Controller.

Figure 3 shows photographs of the original face-to-

face equipment (upper photograph) and the

adaptation of the controller (lower photograph) to

allow its use as a ReLOAD experiment.

A block diagram for the experimental system is

shown in figure 4. When a voltage Demand or Input

signal is applied to the system it passes to the

Forward path potentiometer with variable gain K

set by the user. The signal is then sent to an

amplifier which is then applied to the motor. A

tachogenerator measures the velocity of the motor;

within the VI the magnitude of the velocity feedback

is calculated dependant on the value of a gain K

, set

by the user. The position of the motor is measured

via a potentiometer, with gain K

. This experimental

system allows the user to vary the forward path gain,

, and the feedback gain, K

, and observe the

response of the system in terms of position and

velocity of the servomechanism, hence illustrating

important control concepts. The magnitude of the

position feedback gain is kept fixed at 1 and can not

be altered by the user.

The experiment control software used was

LabVIEW 8.0, the internet server software was

LabVIEW HTTP server 8.0. and the experiment

server was a Pentium 4 cube PC.

Figure 3: The face-to-face experimental rig (upper) and

adaptation for the ReLOAD enabled version (lower).

4 THE CLIENT COMPUTER

The only requirement for the client computer is that

it has appropriate Internet browser software

installed, as only relatively small amounts of data

will be sent to the ReLOAD web server. Upon

entering the experiment internet address, the user is

Output dial

Forward path

potentiometer

Servomechanism

Connections to

Data acquisition

card

Velocity Feedback

Potentiometer

Demand / Input

signal

volts

speed

position

Output Position

(s)

Tachogenerator

Input Voltage

V(s)

)s1(

Integrator

Potentiometer

(Position Feedback)

Gear Box

Amplifier

& Motor

position

volts

Potentiometer

Figure 4: The experiment block diagram.

AN APPLICATION OF REMOTLEY CONTROLLED EXPERIMENTS TO PERFORM FEEDFORWARD AND

FEEDBACK DAMPING CONTROL OF AN ELECTRO MECHANICAL SERVOMECHANISM

423

presented with the Parameters Input web page as

shown in figure 5.

A standard HTML form is used to submit

information to the ReLOAD Web server, with

parameters entered into the text boxes, and

submission activated using the submit button.

Usually a submit button will directly post the

information in a form to the defined address.

However, to prevent the user repeatedly pressing the

submit button, a java-script function first checks to

see if the user has already pressed the submit button.

The form will be submitted only if the function

returns a Boolean ‘true’. Note it would be possible

to remove this java script and use the server

computer to delete duplicate experiment requests.

The results web-page presents the results from

the experiment to the user in a number of ways. A

graph is displayed showing the input signal to the

servomechanism, its displacement, via the voltage

output from a potentiometer, and its velocity,

represented by the voltage output of a tachometer.

An embedded video clip of the experiment and a set

of standard controls allowing replays, rewinding and

fast-forwarding are also displayed. The video is

displayed using a java applet providing a consistent

experience across different browsers and does not

require the user to download any special plugins. A

link to the results Comma Separated Values (CSV)

file is provided allowing them to be imported into

spreadsheet applications such as Excel and a copy to

clipboard function is also included, which serves a

similar purpose. The results web-page is shown in

figure 6.

5 THE EXPERIMENT

Both the face-to-face and ReLOAD delivered

experiments involve two components both utilising a

square wave input signal to drive the

servomechanism. The ReLOAD interface enables the

period of time over which experimental data is

collected to be set as well as the option of a video

clip captured using a standard USB webcam (60fps

320x240). Visualisation of the servomechanisms

motion is a crucial component of understanding the

mathematical parameters used to characterise

dynamic systems.

The first component of the experiment

investigates the effect of varying the forward path

gain, K

, with no velocity feedback, that is K

set to

zero. The user is required to determine the

magnitude of K

which gives the fastest possible

settle time, that is the critically damped state. The

user then chooses two values of K

above and two

values below this critical state and repeats the

experiment. The user should observe that as K

decreased below the critical value, the settle time

increases, there is no overshoot and the damping is

greater than one. Whilst as K

is increased above the

critical value the settle time and overshoot increase

whilst the damping decreases. Students should

observe that varying K

does not alter the magnitude

of the steady state gain. Figure 7 (upper three

graphs) illustrates the response of the

Figure 6: The Results Web-Page.

Figure 5: The Parameter Input Web-Page.

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servomechanism system, in terms of displacement,

to increasing values of K

when K

is zero. The

figure shows two and a half seconds of data with the

first second omitted so as not to show the initial

transient state exhibited by the system, hence

enabling a clearer comparison.

1 1.5 2 2.5 3 3.5

-2

1 1.5 2 2.5 3 3.5

-2

1 1.5 2 2.5 3 3.5

-2

1 1.5 2 2.5 3 3.5

-2

1 1.5 2 2.5 3 3.5

-2

1 1.5 2 2.5 3 3.5

-2

The second component of the experiment

investigates the effect of varying the velocity

feedback gain K

with the forward path gain, K

, set

to a magnitude of 0.5. The user is required, as in the

first component, to determine the magnitude of K

which gives the fastest settle time without any

overshoot, the critically damped state. The user

again chooses two values of K

above and below and

the critical state and observes the percentage

overshoot, settle time, frequency of oscillation and

damping ratio. The students should observe below

the critical damped state as K

is decreased the level

of damping decreases, the settle time, overshoot and

the frequency of oscillation increase. Whilst as the

magnitude of K

is increased above the critical value

the level of damping increases, the settle time

increases and there is no oscillation and the settle

time increases. Figure 7 (lower three graphs)

illustrates the response of the servomechanism

system, in terms of displacement, to increasing

values of K

when K

is set to 0.5.

6 EVALUATION

The particular remote experiment described in this

paper has been used successfully since 2005 as an

alternative to an almost identical face-to-face

version of the Position Servomechanism experiment.

During 2006 the ReLOAD Position Servomechanism

experiment was utilised by number of students at

UCL School of Mechanical Engineering as part of

an assignment.

A servo-motor lab has run at UCL for at least 20

years; 6 sets of experimental apparatus were

originally purchased, and these have been used by

groups of 2 or 3 students at a time. Since its original

purchase, the experimental procedure had become

somewhat outdated: students were asked to change

gains on the controller by interchanging large wire-

wound resistors. Considerable time has been

required to set up the experiments and return them to

storage each year, in addition to the regular

maintenance required to repair natural wear and tear.

In 2006 there was a further pressure of space, as the

control laboratories were being refurbished and

refitted. The combination of these factors meant that

the internet-based laboratory was a very attractive

alternative.

Compared to the traditional laboratory

experiment, the internet-based version has been

continually updated in order to demonstrate the most

current experimental procedure – this was tailored to

be specifically appropriate to the particular course

being taught.

Operating over the internet gave students the

flexibility to study alone or in groups. The lecturer

offered a “surgery session” in a computer cluster,

after a scheduled computer-based class where

students had the opportunity for personal feedback

and guidance in running the experiment. The

queuing system described above worked flawlessly,

and the brief duration of the experiment (approx.10

seconds) meant that students rarely had to wait more

than 20 seconds for their results.

Outside this scheduled session, the system had

the benefits of increasing available experimental

time for the more interested students, and also

increased participation among the less-motivated

students. The experiment was available over the

Figure 7: The servomechanism response to variation of

the forward path and feedback gains.

= 0.015

= 0.030

= 0.050

= 0.1

= 0.4

= 0.6

Effect of varying the forward path gain, K

, excluding

negative velocity feedback, k

= 0.

Effect of varying the negative velocity feedback gain K

with K

= 0.5.

AN APPLICATION OF REMOTLEY CONTROLLED EXPERIMENTS TO PERFORM FEEDFORWARD AND

FEEDBACK DAMPING CONTROL OF AN ELECTRO MECHANICAL SERVOMECHANISM

425

Christmas holiday period, and this gave an

opportunity for students to repeat and check their

results as they wrote their reports. Students

particularly appreciated this opportunity to act on

feedback and guidance from their tutors before

submission of their reports.

An important aspect of the evaluation of this

form of remote experimentation is whether the

learning outcomes of those students undertaking the

experiments remotely are different form those

undertaking face-to-face experiments. A study to

investigate this in detail, would need careful design

to ensure valid comparison. To date, the experiments

performed at UCL and Leeds, though using the same

basic equipment and sharing the same broad

objectives, have been tailored to the individual

institution’s curriculum needs. This has resulted in a

the two institutions setting different learning

objectives for their sessions. This in some way

illustrates the flexibility of the ReLOAD system, but

makes a comparative study problematic. Further

experiments using this system are planned, that it is

hoped will allow this type of direct comparison to be

made.

7 CONCLUSIONS

This paper has illustrated the operating principles of

the ReLOAD system in general and for the remote

delivery of a position servomechanism experiment,

taught face-to-face at The University of Leeds, to a

number of students at University College London.

The pilot study has proved the efficacy of the

ReLOAD system, with both students and lecturers

finding a useful educational tool.

Further development of the ReLOAD system is

underway with a view to improved visualisation and

the delivery of alternative experiments using the

same experimental equipment, alongside the

development of new equipment. Furthermore, the

Higher Education Academy Engineering Subject

Centre has provided funds to build a demonstration

area of the ReLOAD website to raise awareness

amongst UK academics of this new mechanism for

delivering experiments. This will include an

interactive section and teaching materials developed

for use with the experiment.

ACKNOWLEDGEMENTS

The authors would like to thank National

Instruments and the Higher Education Academy

Engineering Subject Centre for their support.

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